The present invention relates to an arrangement comprising a first device being coupled to a second device for exchanging information in a sequence of time slots, said arrangement being arranged for transmitting a signal representing at least one digital symbol from the first device to the second device in a first part of a timeslot and for transmitting a signal representing at least one digital symbol from the second device to the first device in a second part of the timeslot.
The present invention also relates to devices to be used in such an arrangement.
An arrangement according to the preamble is known from the PCT patent application published under number WO 98/488452.
The arrangement according to the above mentioned patent application can be used for interconnection of electronic devices such as integrated circuits on a printed circuit board. In present day systems, it is often required that electronic devices exchange digital information. This can e.g. be control information, or it can be digital information to be passed on by the second device, as is the case in a line interface for a telecommunication device such as a modem.
In general it is desired to use only a small numbers of interconnections between the electronic devices, because this saves pins and external coupling components. To reduce the number of pins and/or the number of external components, in the arrangement according to the prior art, information is transmitted from the first device to the second device during a first part of a timeslot, and information is transmitted from the second device to the first device during a second part of the timeslot.
This way of using the interconnection between the first and second device requires that the second device is synchronized with the first device. This can be done by using a phase locked loop in the second device that locks on the data received from the first device. In the arrangement according to above mentioned patent application in one out of four timeslots a special synchronization sequence is transmitted by the first device to ensure synchronization.
The introduction of the special synchronization sequence has the disadvantage that the timeslot is not completely available for data. Furthermore buffering of data may be necessary to deal with data that is generated in the timeslot being used for synchronization.
The object of the present invention is to provide an arrangement according to the preamble in which the use of the special synchronization sequence is not necessary.
To achieve said object, the arrangement according to the invention is characterized in that the second device comprises control means for terminating the transmission of the at least one digital symbol from the second device to the first device before the end of the second part of the timeslot, and in that the first device comprises further control means for introducing a level change at the beginning of the first part of the time slot.
By terminating the transmission from the second device to the first device before the end of the present timeslot the signal at the input of the second device has a predetermined level at the end of the current timeslot. This makes it possible that the next time slot starts with a level change caused by the transmission of data by the first device. The first device should start its transmission with a level different from the level at the end of the previous timeslot. In this way the second device receives a signal which changes level at the beginning of a time slot. Such a signal is very suitable to synchronize a phase locked loop, making that the special synchronization sequence can be dispensed with.
An embodiment of the present invention is characterized in that the signal representing the digital symbol transmitted in the first part of the timeslot has a same value at the beginning of the first part of a timeslot.
By using a constant value of the signal representing the digital symbol transmitted in the first part of the timeslot, always a same type of edge is present at the beginning of the timeslot. This can be always a rising edge or a falling edge. The use of a same type of edge results in a simplification of the phase locked loop required to synchronize on the received signal.
A further embodiment of the invention is characterized in that the first transmitter is arranged for changing the value of its output signal at an instant within the first part of the timeslot, said instant being determined by the value of the digital symbol to be transmitted.
By encoding a symbol by changing the instant on which the symbol changes, it is obtained that an easy detection of the corresponding symbol is possible in the second device. If the change takes place at a predetermined instant for one symbol value and at a later instant for another symbol value, the value of the transmitted symbol can easily be determined by determining the level of the signal after said predetermined instant but before said later instant.
The arrangement according to the present invention can advantageously be used in a system in which the power required for the second device is (partly) derived from the data signal it receives. In particular this is the case when the communication has to take place over an isolating barrier such as a transformer or a plurality of capacitors. The use of isolating barriers is common in equipment that is connected to the public telephone network such as modems, ISDN or ADSL/HDSL adapters for use in PC""s.